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Clean Water Act Analytical Methods

Whole Effluent Toxicity Methods

Whole Effluent Toxicity (WET) refers to the aggregate toxic effect to aquatic organisms from all pollutants contained in a facility's wastewater (effluent). It is one way we implement the Clean Water Act's prohibition of the discharge of toxic pollutants in toxic amounts. WET tests measure wastewater's effects on specific test organisms' ability to survive, grow and reproduce.

The WET methods listed below are specified at 40 CFR 136.3, Table I A. WET test methods consist of exposing living aquatic organisms (plants, vertebrates and invertebrates) to various concentrations of a sample of wastewater, usually from a facility's effluent stream. WET tests are used by the National Pollutant Discharge Elimination System (NPDES) permitting authority to determine whether a facility's permit will need to include WET requirements.

Acute Toxicity to Freshwater and Marine Organisms

This manual describes test procedures for effluents and receiving waters and includes guidelines on test species selection and mobile toxicity test laboratory design. The acute toxicity tests generally involve exposure of any of 20 test organisms to each of five effluent concentrations and a control water. The test duration ranges from 24 to 96 hours. The following methods are described in the manual (5th edition, 2002).

Chronic Toxicity to Marine and Estuarine Organisms

This manual (3rd edition, 2002) describes five short-term (one-hour to nine-day) methods for estimating the chronic toxicity of effluents and receiving waters to four species. These rules do not apply to discharges into marine waters of the Pacific Ocean.